Bump go.opentelemetry.io/otel/metric from 1.19.0 to 1.20.0 in /examples/demo/server #52067

Job	Run time
setup-environment	0s
govulncheck (receiver-0)	6m 42s
govulncheck (receiver-1)	6m 47s
govulncheck (processor)	2m 39s
govulncheck (exporter)	3m 52s
govulncheck (extension)	3m 6s
govulncheck (connector)	2m 11s
govulncheck (internal)	2m 37s
govulncheck (pkg)	3m 26s
check-codeowners	0s
check-collector-module-version	0s
checks	0s
lint-matrix	0s
unittest-matrix	0s
build-examples	0s
correctness-metrics	0s
correctness-traces	0s
integration-tests	0s
lint	0s
unittest	0s
coverage	0s
cross-compile	0s
build-package	0s
windows-msi	0s
publish-check	0s
publish-dev	0s
publish-stable	0s
rotate-milestone	0s
	31m 20s

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